As someone who has little experience and no preference I can say much in any authoritative fashion. Two things I would consider though that have not been mentioned much:
Do you have programming in the curriculum, maybe even in other degrees that eventually connect with the one you teach in? If so consider the C++ C# difference G mentioned. Do you plan to encourage and offer collateral support for your students that decide to go dip in the deep technical end? Same consideration, make sure they can be supported by someone with experience. Do you have particularly successful or fruitful work placement ties with companies or other unis? If you do what do they prefer? Which of the two is more marketable for the average profile you have created insofar for your students, or the profile you aim to create. Ultimately I don't believe the valuable lessons in game design will be so tightly coupled with the engine you choose that you will do damage either way, much like if you are an extremely good creative or TD you can shine even through an app you're not hugely familiar with and pick it up as you go. All that said, if in doubt to the point of a coin toss decision then look at post-degree consequences of the choice, whichever gives the more immediate edge in employment is likely preferable. Winning the junior employment race for a lot of people that aren't head and shoulders above the average is made of 1% edges.
